This invention relates to a light valve for use in a color display unit which is suitable for image processing by an electronic digital computer, large screen display, and the like.
Such a display unit is used in emitting projection light which is projected on a screen to display a picture. A monochrome display unit is described in an article contributed by Anthony G. Dewey et al to Proceeding of the S.I.D., Volume 19/1 First Quarter 1978, pages 1 to 7, under the title of "Laser-addressed Liquid Crystal Projection Display." According to Dewey et al, the display unit comprises a light valve and has a high resolution, the capability for selective erase, and long-term storage. The light valve is for controlling the projection light.
The light valve has a first and a second principal surface. Incident light is incident onto the first principal surface parallel to an incident optical axis. A laser beam is incident onto the second principal surface and controllably scanned thereon. A part of the laser beam is converted into heat energy in the light valve. The heat energy serves to switch the state of the light valve and to control the incident light in the light valve. The incident light is therefore controlled by the laser beam and is then emitted as controlled light from the first principal surface parallel to an exit optical axis which makes a small angle with the incident optical axis. The controlled light is used as the projection light. The laser beam is used merely because of a high efficiency of the heat conversion. Any other beam may be used so as to be effectively converted to the heat energy. Such a beam will be referred to herein as a controlling beam.
A color display device is disclosed by Keiichi Kubota, one of the present applicants, in Japanese Patent Prepublication No. 107,625 of 1985 which was laid open to public on June 13, 1985. The prepublication is for a Japanese patent application filed by NEC Corporation, the assignee. The color display device is for incident light comprising a plurality of chrominance components. A light valve is included also in the display unit of Kubota and comprises a color filter for dealing with the chrominance components. The color filter comprises a film of either dye or a like organic material. The color filter is therefore not heat resistant. The incident light deteriorates the color filter during a continued use. The color filter therefore has a short life.